Would there be any reason you couldn't use all 6 heroes and gain XP and Credits according to that number at the end of each mission so every single character is properly "Leveled Up", but before each mission you get to choose which 4 you bring along?

We're doing a 1v1 mission so there's no issue with rebel players being attached to their specific character.

This seems like it would be like a lot of RPGs where you choose you're team before starting a mission.

Would this be broken in any way?

I was thinking this would be a really fun way to play the game as well. The heroes are so unique and interesting, but you only get to play with 4 of them in a campaign. Sometimes you realize halfway through a campaign that the heroes you've chosen don't fit your play style or team, or you just want some variety - and it can kinda ruin the whole campaign when you're locked into a character you don't like.

I would suggest that the heroes still only get credits according to each hero that actually goes on the mission. So in most missions that would mean 400 credits (100 x 4 heroes). Because heroes can trade items, you would just give your purchased items to whatever heroes are going in the mission at the time.

The only issue is that you'd have to figure out how to fit in all the character side missions. I suppose with this variant you'd just have to add in an additional 2 hero side missions to the side mission deck.

I love this idea and I'm going to suggest it to my crew for our next campaign. (A rule like this would be even more fun when the expansion comes out too - so we can try out all the heroes without having to do a bunch of campaigns - since each one is so long)

Seems unfair to the Imperial Player unless they can switch their class around during the campaign.

The Imperial player already has access to up to 19 different deployment cards though. That's more than enough variety to keep things fresh AND bring to bear strategies that can exploit the weaknesses of whatever heroes are fielded.

Also, at least in my campaign, the Rebels could use whatever help they can get. They've lost almost every mission haha.

Seems reasonable. Easy enough to house rule such that (for example) if you get captured and have to play a Forced Mission you can't change characters, that sort of thing.

I'd be tempted to give the Imperial player something as well, even if swapping hero characters isn't actually that big a bonus. Swapping Class is the equivalent, and doesn't seem unreasonable.

I'd award money to each hero but then rule that they couldn't share money or swap items.

Once the expansion is out each player could choose 2 hero's and then swap between them.

Swapping classes doesn't really work the same, I'd stick to one class.

I also wonder how using the deployment cards for the spare hero's would work in the campaign.

I think an interesting option (especially once Twin Suns is out and you have 8 heroes) would be that if a hero is wounded/withdraws during a mission, they can't be used in the next one. With this, the Imperial could "choose" what team the Rebels will have in the next mission, at least somewhat.

They spend a mission recuperating. That's a good idea.